I'm pretty sure that the ATX standard (which I don't have a copy of) specify exactly how much capacitance is to be used on the load when measuring noise and ripple, and that capacitance is somewhere >0 F.

well I think the PSU guidelines for ripple measurements just specify some capacitance across the probe tip and not the load. The PSU itself presents a capacitative load at power-on as Travis mentioned and there's a section in the guide for power-on under capacitative loads that it appears to me just simulates the average motherboard capacitor array but I don't think I've ever seen this test done in test results...possibly is implemented in some ATE equipment for programmable dynamic loading though I don't recall.